ANTICIPATORY CONTROL OF UPPER-BODY BALANCE DURING HUMAN LOCOMOTION

Research to date has shown that the large inertial load of the head-arms-trunk (HAT) is controlled within a few degrees in both the frontal and sagittal planes over the gait cycle. Also, there are limited reports of major attenuation of the head anteroposterior (A/P) acceleration in spite of large inertial perturbations at the hips during weight bearing. These findings prompted further investigations into the kinematics and the active control of upper body balance. The first experiment found that the head A/P acceleration was significantly attenuated (0.48 m s-2) compared with the hip (1.91 m s-2) and that the attenuation was gradual from the lumbar level to the neck. A second experiment recorded the EMG profiles of the paraspinal muscles at every second vertebrae level from C-7 to L4. The results demonstrated a 'top-down' anticipatory control which stabilized the head first, then the cervical level, the thoracic level, and finally the lumbar level. Because of the lack of stretching of these paraspinal muscles and the incorrect polarity of the otolith acceleration, it was argued that this balance control was anticipatory and not reflex.